Abstract

Pachytene piRNAs, which comprise >80% of all small RNAs in the adult mouse testis, have been proposed to bind and regulate target RNAs like miRNAs, to cleave targets like siRNAs, or to lack biological function altogether. Although mutants lacking proteins that make pachytene piRNAs are male sterile, no biological function has been identified for any mammalian piRNA-producing locus. Here, we report that loss of piRNA precursor transcription from a conserved pachytene piRNA locus on mouse chromosome 6 (pi6) perturbs male fertility. Loss of pi6 piRNAs has no measurable effect on sperm quantity or transposon repression, yet pi6-/- mice produce sperm with defects in motility, egg fertilization, and embryo development, severely reducing pup production even at the peak of male reproduction. Our data establish a direct role for pachytene piRNAs in spermiogenesis and embryo viability and enable new strategies to identify the RNA targets of individual piRNA species.

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